Optic nerve and chiasmal enhancement in leber hereditary optic neuropathy.

Abstract

To the Editor: Optic nerve enhancement on magnetic resonance imaging (MRI) has been used to help differentiate the acute phase of optic neuritis from Leber hereditary optic neuropathy (LHON). However, retrobulbar optic nerve enhancement with gadolinium administration may occasionally occur in the acute phase of LHON (1). We describe three cases to emphasize that this MRI finding should not dissuade physicians from including LHON in the differential diagnosis of an acute optic neuropathy. Case 1 An 18-year-old man noted painless sequential visual loss in both eyes to count finger visual acuity OD and 20/80 OS. Goldmann perimetry showed large central scotomas OU. Pupils were 7 mm OU with normal reactivity and a 0.9 log unit right relative afferent pupillary defect. Ocular motility was normal. Ophthalmoscopy showed disc elevation with obscuration of the disc margins OU. A detailed neurologic examination was otherwise normal. MRI of the brain and orbits with and without orbital fat suppression and gadolinium showed enhancement of both optic nerves (Fig. 1). Mitochondrial DNA testing revealed a mutation at nucleotide position 3460 compatible with LHON.FIG. 1.: Case 1. T-1 axial (A) and coronal (B) fat-suppressed, enhanced magnetic resonance imaging scan of the orbits shows optic nerve enhancement bilaterally.Case 2 A 7-year-old boy noted bilateral painless visual loss to 20/100 OD and 20/400 OS. Goldmann perimetry showed large central scotomas OU. Pupils were 4 mm OU with normal reactivity and left relative afferent pupillary defect. Ocular motility was normal. Ophthalmoscopy showed disc pallor OU. A detailed neurologic examination was otherwise normal. MRI of the brain and orbits with and without orbital fat suppression and gadolinium showed enhancement of both optic nerves with enlargement of the optic chiasm (Fig. 2). Mitochondrial DNA testing revealed a mutation at nucleotide position 11778 compatible with LHON.FIG. 2.: Case 2. T-1 axial (A) and coronal (B, C) enhanced magnetic resonance imaging scan of the brain shows optic nerve enlargement and enhancement OU and chiasmal enlargement (C).Case 3 A 24-year-old man noted bilateral painless sequential visual loss to 20/300 OU. Automated perimetry showed superior altitudinal and central defects OU. Pupils were 3 mm OU with normal reactivity without a relative afferent pupillary defect. Ocular motility was normal. Ophthalmoscopy showed disc elevation with obscuration of the disc margins with telangiectatic dilated vessels on both optic nerve heads. There was also a blot hemorrhage off the superiotemporal arcade on the right (Fig. 3D). A detailed neurologic examination was otherwise normal. MRI of the brain and orbits with and without orbital fat suppression and gadolinium showed enhancement of both optic nerves (Fig. 3A–C). Mitochondrial DNA testing revealed a mutation at nucleotide position 11778 compatible with LHON.FIG. 3.: Case 3. T-1 weighted axial (A, B) and coronal (C) fat-suppressed, enhanced magnetic resonance imaging scan of the orbits shows optic nerve enhancement OU. Part D shows a blot hemorrhage near the superotemporal arcade in the right fundus.Gadolinium, which does not normally cause optic nerve enhancement by crossing the blood–brain barrier, will do so in pathologic states, which disrupt the blood–brain barrier within the optic nerve (2). An affected optic nerve enhances because gadolinium induces a local magnetic field resulting in a bright signal on T1-weighted fat suppressed images (2). Evidently, bridging of the blood–brain barrier occurs in LHON and in inflammatory optic neuropathies, as we demonstrate here. Our cases had other confounding diagnostic factors, namely enlargement of the optic nerves and chiasm on MRI (Case 2) and retinal hemorrhage on funduscopy (Case 3). Chiasmal enlargement in LHON was recently described in LHON (3); retinal hemorrhage has also been reported, but occurs rarely LHON (4). Acknowledgments This work was supported in part by an unrestricted grant from the Research to Prevent Blindness, Inc. New York, New York; the Fund for the New Jersey Blind, Newark, New Jersey; Lions Eye Research Foundation of New Jersey, Newark, New Jersey; and the Eye Institute of New Jersey, Newark, New Jersey. Michael S. Vaphiades, DO Paul H. Phillips, MD Roger E. Turbin, MD